1. Field of the Invention
The present invention relates to a parallel-plate type substrate processing apparatus using plasma and a substrate processing method.
2. Description of the Related Art
A parallel-plate type substrate processing apparatus includes an upper electrode and a lower electrode disposed in parallel with each other, and generates plasma by applying RF (radio frequency voltage) to the upper electrode or the lower electrode to process a substrate (wafer) placed on the lower electrode by the plasma.
There has been proposed a method to control plasma density and energy of ions entering the substrate from the plasma, by applying RF (radio frequency voltage) and a pulse negative voltage in a superimposed manner to the lower electrode. In this method, the RF controls the plasma density and the pulse negative voltage controls the energy of the ions (see JP-A 2008-85288 (KOKAI)).
However, the recent trend toward a larger diameter of a substrate and a higher density of plasma has led to an increase in the number of ions entering the substrate per unit time. The ions are positively charged, so that the negative voltage applied to the lower electrode is cancelled. This causes a change in the voltage of the substrate held on the lower electrode, leading to a large variation of incident energy of the ions entering the substrate.